1. Technical Field
The present invention relates to an introducer assembly. More particularly, the present invention relates to an introducer sheath and dilator assembly having distal regions of high flexibility for use in accessing a target site in a tortuous portion of the patient's anatomy.
2. Background Information
A variety of well-known medical procedures are carried out by introducing an access device, such as a sheath, into a vessel in a patient's body. Typical procedures for introducing the device include the well-known Seldinger percutaneous entry technique. In the Seldinger technique, a needle is initially injected into the vessel, and a wire guide is inserted into the vessel through a bore of the needle. The needle is withdrawn, and an introducer assembly is inserted over the wire guide into the opening in the vessel. The introducer assembly typically includes an outer introducer sheath and an inner dilator having a tapered distal end. The tapered end of the dilator stretches the opening in the vessel in controlled fashion, so that introduction of the larger diameter introducer sheath may then be carried out with a minimum of trauma to the patient. Following satisfactory placement of the introducer sheath, the dilator is removed, leaving the larger diameter introducer sheath in place in the vessel. An interventional device, such as a catheter, stent, etc., may then be inserted through the introducer sheath into the vessel for placement at a target site within the vasculature.
Historically, these techniques have been problematic, due in large part to the lack of flexibility and/or kink resistance of the sheath. Early sheaths were typically formed of a relatively stiff fluorocarbon, such as polytetrafluoroethylene (PTFE) or fluorinated ethylene propylene (FEP). The sheaths were typically of thin-walled construction, and were prone to kinking, particularly when threaded through tortuous pathways within the body. Increasing the thickness of the sheath only minimally improved the kink resistance of the sheath. At the same time, the added thickness occupied valuable space in the vessel, thereby minimizing the diameter of the interventional device that could be passed therethrough. In addition, increasing the thickness of the sheath necessitated the use of a larger entry opening than would otherwise be required.
A kinked sheath is essentially unusable, and cannot be straightened while positioned in the body of the patient. Consequently, once a sheath kinks, the sheath must be removed, leaving an enlarged, bleeding opening which typically cannot be reused. Access to the vessel must then be re-initiated at an alternative site, and the process repeated with a new sheath. In many cases, a suitable alternative site is not available, and the percutaneous procedure must be abandoned altogether in favor of a different, and often more intrusive, technique.
In recent years, introducer sheaths have been improved in order to enhance their flexibility and kink resistance. Such sheaths are now routinely used to percutaneously access sites in the patient's anatomy that could not be accessed with prior art sheaths. Many such sheaths are also kink resistant through a high degree of bending. One example of a flexible, kink resistant introducer sheath is described in U.S. Pat. No. 5,380,304. The sheath described in this patent includes a lubricious inner liner having a helical coil fitted over the liner. An outer tube is connected to the outer surface of the liner through the coil turns. The sheath described in this patent is thin-walled, and, due to the presence of the coil reinforcement, is kink resistant through a wide range of bending.
U.S. Patent Publication 2001/0034514 discloses an introducer sheath similar in many respects to the sheath of the '304 patent. However, the sheath in the patent publication is formed such that the proximal end of the sheath has a higher stiffness, while the distal end has a lower stiffness. Since the distal portion of the sheath has a lower stiffness (and therefore is more flexible) than the proximal portion, the sheath is able to traverse portions of the anatomy that would have been difficult, if not impossible, to traverse with stiffer sheaths. This sheath has also been found to be kink resistant during a wide range of uses. These patent documents are incorporated by reference herein.
To even further increase the utility of such flexible, kink resistant sheaths, sheaths have now been developed that include one or more predetermined permanent, or semi-permanent, curves at the distal end of the sheath. Examples of such sheaths include the FLEXOR® Introducer Ansel Modification sheath and the FLEXOR® Introducer Balkin Up & Over Contralateral Design, both available from Cook Incorporated, of Bloomington, Ind. These sheaths combine the flexibility and kink resistance of a sheath, such as the sheaths described above, with a precurved distal end.
Curved sheaths are particularly useful for introducing balloons, closed and non-tapered end catheters, stents, and other medical devices into branched or otherwise hard to reach vessels. For example, the curved tip configuration allows access to the renal and contra-lateral iliac arteries from either an iliac or brachial access. This is advantageous for uses such as the delivery of a balloon and/or a stent for branch abdominal aortic aneurysm (AAA) graft placement. The curves of such sheaths may be preformed to any desired configuration, and may be selectively formed to provide access to many otherwise hard-to-reach target vessels. Such sheaths have also been sized for compatibility with either 0.018 inch or 0.038 inch wire compatible dilators.
Although distally curved sheaths have now been successfully used in numerous applications that had previously been problematic with prior non-curved sheaths, some difficulties remain. For example, for optimal results the sheath must be matched with a satisfactory dilator for use in accessing the target area. In order to provide optimal trackability, dilators have typically been formed of a composition, such as PVC, that has a stiffness at least as high as the stiffness of the sheath. The use of a stiff dilator typically causes little or no difficulty when used in combination with conventional straight sheaths. However, such dilators can be problematic when used in combination with a curved sheath, such as a sheath of the type that is used for tracking the iliac bifurcator or tortuous iliacs. In such cases, the stiff dilator has a tendency to straighten out the curve in the sheath. When this occurs, the benefits of using a curved sheath for access to the target site are essentially lost.
It is desired to provide an improved introducer assembly suitable for traversing tortuous passageways in the patient's anatomy. More particularly, it is desired to provide an introducer assembly that combines the benefits available with a curved introducer sheath with a dilator that has a stiffness such that the dilator does not appreciably straighten out the curves in the sheath during use.